This invention relates generally to thermal printing technology, and more specifically to a process of creating background colors in thermal material and the product created thereby, and in particular, to application of the process to produce thermal labels and thermal paper.
Thermal printing is a type of non-impact printing which uses controlled concentrations of heat to develop an image on or in material having a thermal ink deposited thereon. A heated print head is positioned adjacent the thermally coated material, or substrate, which is in most instances paper, in order to cause a desired image to develop on or in the material.
Typically, thermal inks, when dry, appear clear or invisible, but produce an image in a specific color when heated. Thermal inks are typically applied as a one-color selection, meaning images of only one color are produced as the heat source, or heated print head, is applied to the thermally coated material.
If a background color other than white is used in conjunction with a thermal image, the thermal ink is often either coated on top of a colored material, which may have been colored by printing, dying, etc., or mixed with the thermal color ink coating to provide a tinted color background.
Although products are available which produce two colors, such as a black image and a red image, these colors appear as one or the other. Each color is dependent on the heat source developing at a lower temperature vs. a higher temperature. A two color thermally sensitive record material system is disclosed in U.S. Pat. No. 4,151,748.
Turning now to printing techniques, flexographic printing is becoming a common type of printing process in view of letterpress printing. Flexographic printing uses a flexo plate, which is flexible and resilient. The flexographic ink is typically a liquid instead of a paste, and the inking system is straightforward, using a gravure cylinder known as an anilox roll. The anilox roll is inked, wiped clean and transferred onto a raised image area of the flexo plate. The ink remains wet long enough to transfer to the paper or other substrate. Because the flexo plate is resilient, typically made of rubber or photopolymer, it can be impressed against a wide variety of surfaces and can print generally without voids.
Another known printing technique is flood coating, or flooding, which is the printing of a sheet completely with an ink or varnish and involves a process whereby a sponge-like applicator applies a color onto the material.
Tinting paper would screen or add white to a solid color for results of lightening that specific color.